Using-libcurl-with-SSH-support-in-Visual-Studio-2010

Using libcurl with SSH support in 

Visual Studio 2010 

Version 1.3 

© Andrei Jakab (andrei.jakab@tut.fi) 

Using libcurl with SSH support in Visual Studio 2010 1

Revision History 

Revision Date By Comment 

1.0 11 Jul 2011 Andrei Jakab Initial version 

1.1 17 Jul 2012 Andrei Jakab Updated the guide to reflect the latest 

versions of: 

o ActivePerl (5.14.2.1402) 

o libcurl (7.26.0) 

o libSSH2 (1.4.2) 

o NASM (2.10.01) 

o OpenSSL (1.0.1c) 

1.2 22 Sep 2012 Andrei Jakab Appendix A: corrected preprocessor 

definitions 

1.3 05 Feb 2013 Andrei Jakab Updated the guide to reflect the latest 

versions of: 

o ActivePerl (5.16.2.1602) 

o libcurl (7.28.1) 

o libSSH2 (1.4.3) 

o NASM (2.10.07) 


Acknowledgements 

I would like to thank the following people for helping me make this guide what it is today by 

letting me know about typos and by suggesting improvements: 

 

 

 

 

 

 

Chengwei Lin 

Jon Woellhaf 

Philipp Leusmann 

Reinhard Gentz 

Jack Schmidt 

Huu Minh Nguyen 


Table of Contents 

REVISION HISTORY 2 

ACKNOWLEDGEMENTS 3 

CONVENTIONS 5 

1. INTRODUCTION 6 

2. DOWNLOADING THE LATEST SOFTWARE 7 

3. INSTALLATION / COMPILATION 8 

3.1 ActivePerl 8 

3.2 Netwide Assembler 9 

3.3 OpenSSL 9 

3.4 libSSH2 11 

3.5 libcurl 13 

4. USING THE LIBCURL LIBRARY IN YOUR VISUAL STUDIO PROJECT 15 

4.1 Preparing the project’s file structure 15 

4.2 Creating the test project 16 

4.3 How to use the libcurl library 19 

4.3.1 Sample source code 19 

4.3.2 Adding libcurl to the list of libraries 22 

4.3.3 The test-drive 24 

5. FINAL NOTES 25 

APPENDIX A – ADDING OPENSSL SUPPORT DIRECTLY TO LIBCURL 26 


Conventions 

The following font conventions are used in this document: 

 

 

 

 

italic is used for filenames, directory names, and URLs 

constant width is used to indicate commands and code sections 

red, bold and underlined text indicates important items 

bold is used to represent GUI items (e.g. menus, menu items, list nodes etc.) 


1. Introduction 

Libcurl is a widely-used open-source library for transferring files. It supports many protocols 

(e.g. FTP, HTTP, SFTP etc.) and it is very well designed. 

One of libcurl’s strengths is its portability. You can build it on numerous platforms and you can 

be sure that it will work the same way on all of them. This wide support also means that the 

developers cannot constantly update the readme files for all the supported platforms. Thus, I 

have decided to create this document in order to share my experiences while compiling a static 

version of the curl library with SSH support in Visual Studio 2010. 

This document is based on my previous guide “Using libcurl with SSH support in Visual Studio 

2008”, which was inspired from Rosso Salmanzadeh's excellent “Using libcurl in Visual Studio” 

guide. 


2. Downloading the latest software 

Libcurl requires two additional open-source libraries in order to provide the SSH functionality: 

libSSH2 and OpenSSL. Also, since the compilation of OpenSSL makes use of Perl scripts, you 

need to have a Perl distribution installed on your machine. I have chosen ActivePerl, a free 

distribution by ActiveState, for this purpose. OpenSSL also requires the Netwide Assembler to 

be present on your computer. 

The OpenSSL and libSSH2 libraries are distributed as tarballs compressed using gzip. Hence, 

you will need a utility to uncompress and subsequently open the tar file. I recommend the opensource 

archiver 7-Zip. 

In order to obtain the latest version of the Netwide Assembler, click on the link in the table 

below and, on the webpage that appears, follow the link that takes you to the latest stable version 

of NASM. You have the choice between downloading the source code or pre-compiled binaries. 

I strongly encourage you to download the binary files since I will not cover the compilation of 

NASM in this guide. The archives that contain the binary distributions are located in folders 

named after their intended architecture e.g. win32, dos, os2 etc. 

Software URL Current Version 

ActivePerl http://www.activestate.com/activeperl/downloads 5.16.2.1602 

OpenSSL http://www.openssl.org/source 1.0.1c 

libSSH2 http://www.libssh2.org 1.4.3 

libcurl http://curl.haxx.se/download.html 7.28.1 

Netwide Assembler http://www.nasm.us 2.10.07 

7-Zip http://www.7-zip.org 9.20 

NOTE: This guide assumes that you already have successfully installed Microsoft Visual 

Studio 2010 (VS2010). The examples in this document were built using version 

10.0.40219.1 SP1 of VS2010. 


3. Installation / Compilation 

3.1 ActivePerl 

Installing ActivePerl is fairly straightforward as long as you are logged in with an Administrator 

account. Below are screenshots from each step of the installation process. Please pay particular 

attention to Step 4 because choosing the wrong option there will make your life harder later. 

Step 1 - Introduction 

Step 2 - EULA 

Step 3 - Customization 1 

Note 1: The “Documentation” and 

“Examples” are only useful if you 

wish to learn how to use ActivePerl; 

for the purposes of this document, 

these items are not needed. 

Note 2: The default installation location is not 

in the Program Files folder. Make sure 

to change this if you like to keep your 

C: folder tidy. 

Step 4 - Customization 2 

NOTE: Make sure that there’s a checkmark 

besides the “Add Perl to the PATH 

environment variable” option. 


Step 5 - Installation Confirmation 

Step 6 - Installation Complete 

3.2 Netwide Assembler 

1. Extract the nasm-2.10.07 folder from the zip file and place it in the C: root directory 

3.3 OpenSSL 

Compiling the OpenSSL library is a bit tricky. The following step-by-step guide should help you 

get through the compilation process as quickly and as painlessly as possible. 

1. Extract the openssl-1.0.1c.tar file from the gzip file to a temporary directory 

2. Extract the openssl-1.0.1c folder from the tar file and place it in the C: root directory 

3. Close the VS2010 IDE and open a Visual Studio 2010 command prompt. If you’ve 

installed VS 2010 with the default settings, the command prompt shortcut should be 

located in Start -> All Programs -> Microsoft Visual Studio 2010 -> Visual Studio 

Tools -> Visual Studio Command Prompt (2010) 

4. Add the NASM executable to the PATH environment variable: 

path = %PATH%;C:\nasm-2.10.07 

5. Create the directory where the output of the compilation process will be stored: 

mkdir c:\openssl_lib 

6. Change the working directory to the OpenSSL directory: 

cd /D c:\openssl-1.0.1c 

7. Configure the OpenSSL installation with: 

perl Configure VC-WIN32 --prefix=c:/openssl_lib 

where the --prefix argument specifies where OpenSSL header and library files will 

be copied at the end of the compilation process. 

NOTE: The path that is passed to the --prefix argument must be in the UNIX 

format i.e. forward slashes are used to separate directories and not backward 

slashes like it is customary in Windows. 


The output of this command should look like this: 

8. Create the required assembly files: 

ms\do_nasm 

Note: Using assembly files makes the execution of library functions much faster. If you 

do not wish to use assembly files, use the following command instead and jump to 

step 8: 

ms\do_ms 

9. Compile the static library: 

nmake -f ms\nt.mak 

10. The compilation process takes a while so you can go grab some coffee/tea at this point. 

11. If all is well, at the end of the compilation you will have some libraries and a number of 

executables in C:\openssl-1.0.1c\out32 

12. The library contains some built in tests that allow you to check if everything has 

compiled properly and if the library is in working order: 

nmake -f ms\nt.mak test 

If the library has compiled properly, you should obtain a “passed all tests” message once 

this command finishes executing. 

13. To install OpenSSL to the location you specified in step 6, run: 

nmake -f ms\nt.mak install 

Note: You can find additional compiling instructions in C:\openssl-1.0.1c\INSTALL.W32; this 

file also contains a troubleshooting section that could help you out if something goes 

wrong during the compilation process. 


3.4 libSSH2 

1. Extract the libssh2-1.4.3.tar file from the gzip file to a temporary directory. 

2. Extract the libssh2-1.4.3 directory from the tar file and place it in the C: root directory. 

3. Open C:\libssh2-1.4.3\win32\libssh2.dsp in the Visual Studio 2010 IDE. Since this 

project file was created using an older version of Visual Studio, the following message 

box will appear: 

Click on “Yes”. Once the conversion is completed, you should see the following in the 

Solution Explorer window: 


4. Set the LIB Debug as the active solution configuration. On the Build menu in Visual 

Studio, click Configuration Manager… and in the window that appears select LIB 

Debug from the Active solution configuration drop-down list. Close the Configuration 

Manager. 

5. Next, you must tell the compiler and the librarian where the OpenSSL library is located 

and how to compile the library: 

a. Right-click on the libssh2 project in the Solution Explorer window and select 

Properties from the pop-up menu. 

b. Expand the Configuration Properties node, click on the C/C++ node 

i. Select General, choose the Additional Include Directories property and 

add the following: 

;C:\openssl_lib\include 

(the semicolon needed since other paths are already present) 

ii. Next, click on Code Generation and in the Runtime Library field, select 

the Multi-threaded Debug DLL (/MDd) option. 

c. Also in the Configuration Properties node, expand the Librarian node, and 

select General. 

i. Change the Output File property to: 

Debug_lib\libssh2.lib 

ii. Click on the Additional Dependencies property and set it to: 

libeay32.lib;ssleay32.lib 

iii. Choose the Additional Library Directories and add the following path: 

C:\openssl_lib\lib 

d. Click on the OK button. 

6. Now we are ready to compile. Right-click on the libssh2 project and select Build from 

the pop-up menu. VS2010 will prompt you to save the solution file that was created for 

this project. Once you save it, compilation will begin. 

7. The compiler might display a couple of security warnings and/or “possible loss of data” 

warnings. Also the linker might display a number of LNK4221 warnings. For our 

purposes, both of these types of warnings can be safely ignored. 


3.5 libcurl 

1. Extract the curl-7.28.1 folder from the archive and place it in the C: root directory. For 

our purposes, we will need the files located in the lib and include directories. 

2. Open C:\curl-7.28.1\lib\libcurl.vcproj in the Visual Studio 2010 IDE. Since this is a 

Visual Studio 2005 project file, the “Visual Studio Conversion Wizard” will appear. The 

wizard should not encounter any problems converting the project to the VS2010 format 

but will generate a couple of warnings, which can be safely ignored. 

3. Next, you must tell the compiler and the librarian to use the libSSH2 library and where 

this library is located: 

a. Right-click on the libcurl project in the Solution Explorer window and select 


b. Expand the Configuration Properties node, then the C/C++ node. 

i. Click on the General node. Next to Additional Include Directories, add 

the following: 

;C:\libssh2-1.4.3\include 

(the semicolon is needed since there are already two additional include 

directories specified) 

ii. Select the Preprocessor node and click on the Preprocessor Definitions 

property. Add in the following to the existing definitions: 

;CURL_STATICLIB;USE_LIBSSH2;CURL_DISABLE_LDAP;HAVE_ 

LIBSSH2;HAVE_LIBSSH2_H;LIBSSH2_WIN32 ;LIBSSH2_LIBRARY 

c. In the Configuration Properties node, expand the Librarian node, and select 

General. 

i. Select Additional Dependencies and type in: 

libssh2.lib 

ii. Next to Additional Library Directories, type in the path: 

C:\libssh2-1.4.3\win32\Debug_lib 

d. Click on the OK button. 

4. After all this work, we are finally ready to compile the libcurl library. Right-click on the 

curllib project in the Solution Explorer and select Build from the pop-up menu. VS2010 

will prompt you to save the solution file that was created for this project. Once you save 

it, compilation will begin: 

1>------ Build started: Project: libcurl, Configuration: Debug Win32 ------ 

1> wildcard.c 

1> warnless.c 

1> version.c 

1> url.c 

1> transfer.c 


1> timeval.c 

… 

1> curl_darwinssl.c 

1> curl_addrinfo.c 

1> cookie.c 

1> content_encoding.c 

1> Generating Code... 

1> Compiling... 

1> connect.c 

1> base64.c 

1> axtls.c 

1> asyn-thread.c 

1> asyn-ares.c 

1> amigaos.c 

1> Generating Code... 

1>libssh2.lib(ecp_nistputil.obj) : warning LNK4221: This object file does not define any 

previously undefined public symbols, so it will not be used by any link operation that 

consumes this library 

1>libssh2.lib(ecp_nistp521.obj) : warning LNK4221: This object file does not define any 









1>libssh2.lib(fips_ers.obj) : warning LNK4221: This object file does not define any 



1> libcurl.vcxproj -> C:\curl-7.28.1\lib\.\Debug\libcurl.lib 

========== Build: 1 succeeded, 0 failed, 0 up-to-date, 0 skipped ========== 

The LNK4221 warnings can be safely ignored. 

By default, the output directory is C:\curl-7.28.1\lib\Debug. In order to create an 

application that uses the libcurl library, we only need the libcurl.lib file from the output 

directory and the C:\curl-7.28.1\include\curl directory, which contains the library’s 

header files. 


4. Using the libcurl library in your Visual Studio project 

In this section we will create a test project, which will at the same time test the library’s 

functionality and demonstrate how to integrate libcurl into one of your projects. I suggest that 

you follow the example step by step (i.e. use the same project names, paths etc.) so that you 

obtain the same figures as the ones shown below. This will make your life easier in case you 

encounter any problems along the way. 

4.1 Preparing the project’s file structure 

Create the following folder structure in you C: root directory: 

Copy the curl folder from the C:\curl-7.28.1\include directory into the C:\Projects\custom 

libraries\include directory. The curl directory should contain the following files: 

Notice that there are also 4 make files in this directory. We won’t need them so they can be 

safely deleted, if you wish. 

Finally, you need to copy liburl.lib from C:\curl-7.28.1\lib\Debug to C:\Projects\custom 

libraries\lib_dbg. 


4.2 Creating the test project 

The libcurl library can be used in any type of application. In order to keep things simple, we will 

create a simple Win32 console application. 

1. Fire up VS2010 and go to: File -> New -> Project… 

2. First expand the Visual C++ node, then select the Win32 node and click on the Win32 

Console Application item in the middle panel: 

3. Type in “test_curl” for the project name. The project location should be: 

C:\Projects 

Make sure that the checkbox Create directory for solution is checked and click on OK. 


4. The Win32 Application Wizard will appear. In the first window click on Next: 

5. In the following window: 

a. Make sure that Console application is selected from the Application type: list 

b. In Additional options, uncheck the Precompiled header option. 

c. Ensure that both ATL and MFC are unchecked in the Add common header files 

for: list. 

Now you can press on the Finish button and wait for VS2010 to set up your project. 


6. In the Solution Explorer window you should see the following project structure: 

Double-click on test_curl.cpp to open it (if VS2010 didn’t already do so for you). The 

source code should look like this: 


4.3 How to use the libcurl library 

4.3.1 Sample source code 

Replace all the code in test_curl.cpp with this code: 

// headers 

#include "stdafx.h" 

#include 



// prototypes 

int 

libcurl_progress_callback (void * clientp, double dltotal, 

double dlnow, double ultotal, 

double ulnow); 

size_t libcurl_read_callback(void * pBuffer, size_t size, size_t nmemb, 

void * hFile); 

void SSHUpload(char * strFileName, char * strFilePath); 

int _tmain(int argc, _TCHAR* argv[]) 

{ 

SSHUpload("test.txt", "C:\\"); 

printf("Press any key to continue..."); 

_getch(); 

} 

return 0; 

void SSHUpload(char * strFileName, char * strFilePath) 

{ 

char strBuffer[1024]; 

CURL * hCurl; 

CURLcode ccCurlResult = CURL_LAST; 

curl_off_t cotFileSize; 

HANDLE hFile; 

LARGE_INTEGER liFileSize; 

// check parameters 

if((strFileName == NULL || strlen(strFileName) == 0) || 

(strFilePath == NULL || strlen(strFilePath) == 0)) 

return; 

// parse file path 

if(strFilePath[strlen(strFilePath) - 1] == '\\') 

sprintf_s(strBuffer, 1024, "%s%s", strFilePath, strFileName); 

else 

sprintf_s(strBuffer, 1024, "%s\\%s", strFilePath, strFileName); 

// create a handle to the file 

hFile = CreateFileA(strBuffer, 

GENERIC_READ, 

FILE_SHARE_READ, 

NULL, 

OPEN_EXISTING, 

FILE_ATTRIBUTE_NORMAL, 

NULL); 

// file to open 

// open for reading 

// share for reading 

// default security 

// existing file only 

// normal file 

// no attr. template 


if(hFile != INVALID_HANDLE_VALUE) 

{ 

// global libcurl initialisation 

ccCurlResult = curl_global_init(CURL_GLOBAL_WIN32); 

if(ccCurlResult == 0) 

{ 

// start libcurl easy session 

hCurl = curl_easy_init(); 

if(hCurl) 

{ 

// enable verbose operation 

curl_easy_setopt(hCurl, CURLOPT_VERBOSE, TRUE); 

// enable uploading 

curl_easy_setopt(hCurl, CURLOPT_UPLOAD, TRUE); 

// inform libcurl of the file's size 

GetFileSizeEx(hFile, &liFileSize); 

cotFileSize = liFileSize.QuadPart; 

curl_easy_setopt(hCurl, 

CURLOPT_INFILESIZE_LARGE, 

cotFileSize); 

// enable progress report function 

curl_easy_setopt(hCurl, CURLOPT_NOPROGRESS, FALSE); 


CURLOPT_PROGRESSFUNCTION, 

libcurl_progress_callback); 

// use custom read function 


CURLOPT_READFUNCTION, 

libcurl_read_callback); 

// specify which file to upload 

curl_easy_setopt(hCurl, CURLOPT_READDATA, hFile); 

// specify full path of uploaded file (i.e. server 

// address plus remote path) 

sprintf_s(strBuffer, 

1024, 

"sftp://123.123.123.123/home/user/%s", 

strFileName); 

curl_easy_setopt(hCurl, CURLOPT_URL, strBuffer); 

// set SSH server port 

curl_easy_setopt(hCurl, CURLOPT_PORT, 22); 

// set SSH user name and password in libcurl in this 

// format "user:password" 


CURLOPT_USERPWD, 

"user:password"); 

// set SSH authentication to user name and password 


} 

} 


CURLOPT_SSH_AUTH_TYPES, 

CURLSSH_AUTH_PASSWORD); 

// execute command 

ccCurlResult = curl_easy_perform(hCurl); 

// end libcurl easy session 

curl_easy_cleanup(hCurl); 

} 

} 

else 

// release file handle 

CloseHandle(hFile); 

// global libcurl cleanup 

curl_global_cleanup(); 

if (ccCurlResult == CURLE_OK) 

printf("File uploaded successfully.\n"); 

else 

printf("File upload failed. Curl error: %d\n", 

ccCurlResult); 

printf("File upload failed! Could not open local file"); 

size_t libcurl_read_callback(void * pBuffer, size_t size, 

size_t nmemb, void * hFile) 

{ 

DWORD dwNumberOfBytesRead = 0; 

BOOL bResult = ReadFile((HANDLE) hFile, pBuffer, size * nmemb, 

&dwNumberOfBytesRead, NULL); 

} 

return dwNumberOfBytesRead; 

int libcurl_progress_callback (void * clientp, double dltotal, double dlnow, 

double ultotal, double ulnow) 

{ 

printf("Uploaded: %d / %d\n", (int) ulnow, (int) ultotal); 

} 

return 0; 

NOTE: You must replace some of the information in the sample code: 

line 17: enter a file name to be uploaded and its location on your computer 

line 93: type in your server’s IP address and the remote path where the file should 

be stored (here I assume that you have access to a computer that is 

running a SSH server) 

line 104: the login credentials for the SSH server 


4.3.2 Adding libcurl to the list of libraries 

Now let’s tell the compiler where to find the libcurl header files and the library itself: 

1. In the Solution Explorer window, right-click on the test_curl project window and select 


2. Expand the Configuration Properties node. 

3. Expand the C/C++ node 

a. Select the General node, choose the Additional Include Directories property 

and add the path: 

C:\Projects\custom_libraries\include 

NOTE: While you might be tempted to include the "C:\Projects\custom 

libraries\include\curl" directory instead, we must add the parent directory 

since some libcurl files use #include statements like this one: “#include 

”. 


. Select the Preprocessor node and click on the Preprocessor Definitions 


;CURL_STATICLIB 

4. Expand the Linker node. 

a. Select the General node, chose the Additional Library Directories property and 

add the path: 

C:\Projects\custom_libraries\lib_dbg 


. Select the Input node, click on the Additional Dependencies property and add 

the following to the existing list of libraries: 

;libcurl.lib;ws2_32.lib 

5. Click on the OK button. 

4.3.3 The test-drive 

Now we are finally ready to reap the fruits of our labor: compile and run the program. Depending 

on the size of the file you chose to upload, the output should look similar to the figure on the 

next page. 


5. Final Notes 

Congratulations! You are now ready to use libcurl in your own projects. If you run into trouble 

down the road, don’t hesitate to post a message on libcurl’s very active mailing list: 

http://cool.haxx.se/mailman/listinfo/curl-library. However, please take a moment and read the 

mailing list etiquette (http://curl.haxx.se/mail/etiquette.html) before posting. 


Appendix A – Adding OpenSSL support directly to libcurl 

Some of you might find it useful to have SSL/TLS support directly built into libcurl. In this case, 

compilation procedure that was presented in section 3.5 is identical with the exception of step 3, 

which must be replaced with the following: 

3. Next, you must tell the compiler and the librarian to use the OpenSSL library and where 

this library is located: 

a. Right-click on the libcurl project in the Solution Explorer window and select 


b. Expand the Configuration Properties node, then the C/C++ node. 

i. Click on the General node. Next to Additional Include Directories, add 

the following: 

;C:\libssh2-1.4.3\include;c:\openssl_lib\include\;c:\openssl_lib\include\openssl 

(the semicolon is needed since there are already two additional include 

directories specified) 

ii. Select the Preprocessor node and click on the Preprocessor Definitions 


;CURL_STATICLIB;USE_LIBSSH2;CURL_DISABLE_LDAP;HAVE_ 

LIBSSH2;HAVE_LIBSSH2_H;LIBSSH2_WIN32 

;LIBSSH2_LIBRARY;USE_SSLEAY;USE_OPENSSL 

c. In the Configuration Properties node, expand the Librarian node, and select 

General. 

i. Select Additional Dependencies and type in: 

libssh2.lib;libeay32.lib;ssleay32.lib 

ii. Next to Additional Library Directories, type in the path: 

C:\libssh2-1.4.3\win32\Debug_lib;c:\openssl_lib\lib 

Since the OpenSSL library was already included as part of the libSSH2 compilation, at the end 

of the libcurl compilation, the linker will present a whole bunch of “second definition ignored” 

warnings, which can be safely ignored.

Using-libcurl-with-SSH-support-in-Visual-Studio-2010

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